What does Brooks mean by Representation?
First, Pascal is not a logic programming language. Logic programming refers to languages like Prolog where you have a declarative style of programming compared to a imperative style like you have in Pascal. Maybe you mean if-statements which are typical for imperative languages.

Second, representation means a certain level of abstraction. For instance, a model represents a certain part of the reality. Imagine a cup on a table. If the agent has a representation of this situation, it has a symbol table and a symbol cup which represents the things in the real world. Now it can have a relation on(cup, table) which represents the situation that the cup is on the table. This type of abstraction can be easily represented in a logic language like first order logic. Therefore, one uses logic programming languages like Prolog or other types of languages like OWL to represent knowledge and perform reasoning. So the important term to which Brooks refers is Knowledge Representation and Reasoning.

Third, if your agent only have sensor data like video or sonar data, then it knows only distances or pixels from the real world. That is not meant with representation. Brooks' Creatures have only this information and calculate with this data directly to perform an action without reasoning. In that sense also artificial neural networks have no representation.

Finally, for an open source project to understand representation I would recommend the above mentioned OWL. You can look at the Protégé editor for working with OWL. In an OWL ontology you can represent relations between things and reason about them.